The present invention relates to a method of controlling the viscosity of fabric softening compositions and, more particularly, to a method for avoiding gelation or gel formation of fabric softener compositions.
Fabric softening agents are used in order to improve the feel and texture of fabrics and to improve the comfortability of fabrics in actual wear. More particularly, fabric softeners have the effect of reducing the static charge on man-made fabrics and give a softer feel to cotton articles. They usually contain from 4-8% cationic detergent material and are pourable, easily-dispersed liquids. Sodium chloride or acetate are used to lower the viscosity while addition of methylcellulose or long chain alcohol increases viscosity. The structures responsible for viscosity are the multiwalled vesicles (similar to liposomes) formed by the surfactant. If small amounts of ionic or non-ionic materials are added to the system slow osmotic swelling or shrinkage of the vesicles can occur leading to marked changes in viscosity on storage. As the concentration of the surfactant increases in the fabric softener, the concentration and size of the vesicles increases. Therefore rheological behavior becomes a real issue for the product.
Typically, fabric softening agents are applied from an aqueous liquid which is made up by adding a relatively small amount of a fabric softening composition to a large amount of water, for example during the rinse cycle in an automatic washing machine. The fabric softening composition is usually an aqueous liquid product containing between about 8% and 25% of a cationic fabric softening agent which is a quaternary ammonium salt. Such compositions are normally prepared by dispersing in water a cationic material, for example quaternary ammonium compounds which in addition to long chain alkyl groups may also contain ester or amide groups. It is also advantageous to use mixtures of different fabric softening components which are typically added to the last wash cycle rinse both in the form of aqueous dispersions.
It is widely known that fragrances can be introduced into liquid fabric softener compositions in order to cause the treated fabrics to have aromas with good initial strength. Efforts have also been made to develop systems in which aromas are controllably released during the normal conditions of use of the fabrics treated with solutions created from the liquid softening compositions of matter at a predictable sufficiently high level over an extended period time.
It is recognized in the prior art that perfume containing particles of a defined melting point and size can be incorporated into compositions containing fabric softening components. Typical of such prior art is Canadian Patent 1,111,616, German OLS 2631129, German OLS 2702162, U.S. Pat. Nos. 4,234,627 and 4,464,271.
Since the early '80's, fabric softeners have been on the market in a concentrated form of one type or another. Normal concentrations for fabric softeners typically range from 3 to 7% active ingredients. The concentrates came into the market at 3 to 6 times the normal surfactant concentration. Thus the concentrated forms of fabric softeners can contain 10 to 50% surface active agent.
However it has been found that when the amount of fragrance is increased beyond just one, two or three percent, there is a tendency for the fabric softener base formulation to gel. Undesirable gelation of the fabric softener reduces the shelf life of the product and may cause an adverse consumer reaction when the person using the fabric softener opens the container and finds that the fabric softener has formed a gel like, highly viscous mass instead of being free flowing.
This tendency of gel formation has prevented the utilization of larger amounts of fragrances or the use of large amounts of fragrances with a relatively weak aroma creating power.
Various efforts have been made to influence the viscosity of fabric softeners to overcome certain problems and to improve properties. For example, low viscosity concentrated products as shown in U.S. Pat. No. 3,681,241 contain ionizable salts, fatty acids, fatty alcohols, fatty esters and paraffinic hydrocarbons. See also European patent 13780.
It has also been proposed in European patent specification 56695 to control the viscosity of concentrated products by the use of small amounts of alkoxylated amines.
Still further developments are shown in U.S. Pat. No. 4,497,716 where there is disclosed a concentrated liquid fabric softening composition which contains a water soluble cationic fabric softening agent, a nonionic viscosity control agent and an electrolyte. The viscosity control agent is an alkylene oxide adduct of a fatty compound selected from fatty amines, fatty alcohols, fatty acids and fatty esters.
It is therefore an object of the present invention to provide a way to avoid gelation in fragrance containing fabric softening agents and also to provide a way to permit the introduction of an increased amount of fragrance into a fabric softening composition.